Integrated circuit wiring method

ABSTRACT

Wiring an IC, using flexible circuits, by relating a circuit board to an IC and using traces on the circuit board as a second set of input to the IC. More specifically, a set of first lands on the circuit board are connected to a first set of lands on the IC. The circuit board and IC are positioned so as to present a second set of lands on the circuit board in close proximity to a second set of lands on the IC. A first flex circuit is connected to the second lands on the circuit board while a second flex circuit is connected to the second lands on the IC. The flex circuits may be connected to signal wires or may serve themselves as the main signal wires.

This is a continuing application under 37 CFR 1.53(b) of priorapplication Ser. No. 09/919,238, filed Jul. 31, 2001 now U.S. Pat. No.6,582,371 of DAVID G. MILLER for ULTRASOUND PROBE WIRING METHOD ANDAPPARATUS.

BACKGROUND OF THE INVENTION

The present invention relates to apparatus and methods for connectingelectrical leads (wires, traces, etc . . . ) to a device and inparticular to apparatus and methods for connecting a large number ofleads to a device contained in a relatively small area, such as an ICchip in a housing for a transesophageal ultrasound probe.

Non-invasive, semi-invasive and invasive ultrasound probes have beenwidely used to view tissue structures, such as the heart, the abdominalorgans, the fetus, and the vascular system. Semi-invasive systemsinclude transesophageal imaging systems, while invasive systems includeintravascular imaging systems. Depending on the type and location of thetissue, different systems provide better access to or improved field ofview of internal biological tissue.

An ultrasound probe usually comprises at least one transducer element,typically formed of PZT material, and may comprise a one or twodimensional array of such elements. In general, each element must beconnected to a separate lead and a common ground plane. Since many ofthe proposed two dimensional arrays have a significant number ofelements (for example even a relatively small 56×56 array has 3,136elements) the number of required connections is quite large. Formingconnections between the drive circuits and such an array of elements hasproven challenging.

One of the more specialized types of ultrasound probes is thetransesophageal probe (TEE Probe) which is formed on a long slender bodyplacing sever limitations on the mechanical and electrical designthereof. Specifically, TEE probes have considerable space constraintsthat must be observed when designing the probe. This affects not onlythe size of the elements (and therefore the array), but also the volumeavailable to connect the leads to the array. While known one-dimensionalarrays typically have a fine horizontal pitch with a coarse verticalpitch, many proposed two dimensional arrays are finely pitched in bothdirections having horizontal and vertical measurements of less than 5mm. In a non-invasive probe, adequate room for such connection may becreated, but in an invasive probe, such as a TEE probe, space isseverely limited and every square nanometer is valuable. It has beenextremely difficult to design a TEE probe which provides a significantnumber of discrete leads within the space allowed by the overall designof the probe and more importantly it has proven difficult to connect anysignificant number (such as are required for a 2-D transducer assembly)of leads to their respective elements in the array. Traditionalconnections either require too much space or are too difficult toimplement as part of an assembly process.

The present inventor has invented a method and apparatus permitting theconnection of a large number of leads to a device wherein suchconnections must be implemented in a relatively small area. Such methodsand apparatus are well adapted for use with TEE probes and otherultrasound probes.

BRIEF DESCRIPTION OF THE DRAWINGS

An understanding of the present invention can be gained from thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings of which:

FIG. 1 is an illustration of an ultrasound system including atransesophageal imaging probe.

FIG. 2 is a plan view of a flexible circuit in accordance with apreferred embodiment of the present invention.

FIG. 3 is an enlarged partial view of the flexible circuit shown in FIG.2.

FIG. 4 is a cross-sectional view of the flexible circuit of FIG. 2.

FIG. 5 is a cross-sectional view of a transesophageal imaging probe inaccordance with the preferred embodiment of the present invention.

FIG. 6 is a top down cross-sectional view of the transesophageal imagingprobe shown in FIG. 5 in accordance with the preferred embodiment of thepresent invention.

FIG. 7 is a cross-sectional view of the transesophageal imaging probeshown in FIG. 5 taken along line B—B shown in FIG. 6.

FIG. 8 is a diagram of connections between the flexible circuit shown inFIG. 2 and the circuit board and the IC shown in FIG. 5.

FIG. 9 is a diagram of connections between the circuit board shown inFIG. 5 and the IC also shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the present invention, anexample of which is illustrated in the accompanying drawings, whereinlike reference numerals refer to like elements throughout.

While the apparatus set forth in the present application is described asbeing specifically constructed for ultrasound imaging, the methods andapparatus recited herein may be used to solve a variety of similarproblems (a large number of connection in a limited volume) in otherfields. The methods and apparatus presented herein are not inherentlyrelated to any particular ultrasonic system, computer or otherapparatus. Devices which may benefit from the present invention includethose manufactured AGILENT TECHNOLOGIES.

FIG. 1 is an illustration of an ultrasound system 10 including atransesophageal imaging probe 12. The ultrasound imaging system 10includes the transesophageal probe 12 (referred to herein as a “TEEprobe”) with a probe handle 14, connected by a cable 16, a strain relief17, and a connector 18 to an electronics box 20. Electronics box 20 isinterfaced with a keyboard 22 and a video display 24. The electronicsbox 20 generally includes a transmit beamformer, a receive beamformer,and an image generator. TEE probe 12 has a distal part 30 connected toan elongated semi-flexible body 36. The proximal end of elongated part36 is connected to the distal end of probe handle 14. Distal part 30 ofprobe 12 includes a rigid region 32 and a flexible region 34, which isconnected to the distal end of elongated body 36. Probe handle 14includes a positioning control 15 for articulating flexible region 34and thus orienting rigid region 32 relative to tissue of interest.Elongated semi-flexible body 36 is constructed and arranged forinsertion into the esophagus. The entire TEE probe 12 is about 110 cmlong and is about 9 mm in diameter.

FIGS. 2 through 4 show a flexible circuit 100 (also referred to hereinas a “flex circuit 100”) in accordance with the preferred embodiment ofthe present invention. FIG. 2 is a plan view of the flex circuit 100 inaccordance with a preferred embodiment of the present invention, andmore specifically shows the flex circuit 100 in an “unfolded” position.The flex circuit 100 serves to connect leads, typically small diameterco-axial cables, from the elongated semi-flexible body 36 (see FIG. 1)to transducer elements and may, for example, be constructed inaccordance with the teachings of U.S. Pat. No. 5,296,651, owned by theassignee of the present invention and incorporated herein by reference.In accordance with such teaching, the flex circuit 100 may, but notnecessarily, be provided with a ground plane (not shown).

The flex circuit 100 has a first end 110 comprised of leads 110 a-110 nfor electrical connection to a structure such as an IC chip. In general,an element reference with just a number refers to a unitary whole or acollection of elements, while an element reference with a number and aletter refers to individual elements of the collection (typically anindividual leads). The leads 110 a-110 n on the first end 110 arepreferably spaced to have a pitch of 110 micrometers. This densitypermits the use of tape-automated bonding (TAB), preferably utilizingthermosonic welding, to physically construct the required connections.To facilitate TAB bonding, the leads 110 a-110 n of the flex circuit 100may be formed so as to overhang or cantilever.

Opposite the first end 110, the leads in the flex circuit 100 aredivided into three branches, a first outer branches 112 a second outerbranch 113 and a center branch 114. The example shown in FIG. 2 has: 20signal lines 112 a-112 t in the outer branch 112; 20 signal lines 113a-113 t in outer branch 113; and 40 signal lines 114 a-114 nn in thecenter branch 114. The number of lines was selected more for symmetryand ease of explanation and can easily be varied based on need and/ordesign limitations. The leads in each of the branches 112, 113, and 114are spread apart to facilitate connection to a plurality of smalldiameter co-axial cables 116 a through 116 n (for ease of explanationthe description that follows herein will typically refer to theplurality of co-axial cables as cables 116). As shown in FIG. 2, theincrease in pitch of the individual traces is accomplished using two 90°bends. The leads in the three branches 112, 113, and 114 preferably havea pitch of 200 micrometers facilitating connection to the co-axialcables 116.

In this manner, a single flex circuit 100 can provide connections to atleast 80 cables 116 as shown in FIG. 2. Additionally, in accordance withthe teachings of the '651 patent discussed herein above, the flexcircuit 100 may be provided with a ground plane. Those of ordinary skillin the art will recognize that the exact configuration of the flexcircuit 100, including the number of leads and the presence of a groundplane, may be modified to suit a variety of factors, including cost,number of signal channels, required flexibility, etc . . .

FIG. 3 is an enlarged partial view of the flexible circuit 100 shown inFIG. 2. FIG. 3 illustrates some of the detail of the connections betweenthe co-axial cables 116 and the flex circuit 100. Each of the coaxialcables 116 a-116 n are preferably stripped, tinned, and soldered to theflex circuit 100. Each of the coaxial cables 116 are soldered at twolocations: an exposed inner conductor 117; and an exposed outerconductor 118. Each of the inner connectors 117 are soldered to aseparate lead of the flexible circuit 100, for example lead 116 a. Eachof the outer conductors 118 may be soldered to a ground plane (notshown) of the flex circuit 100. Of course, if the flex circuit 100 doesnot include a ground plane, each of the outer connectors 118 may beelectrically tied together and connected to an external ground plane,such as a copper foil, using any of a variety of methods known to thoseof ordinary skill in the art. Alternatively, each of the outerconnectors 118 can be used as a signal path with other arrangementsbeing made for ground (such as a dedicated signal path).

FIG. 4 is a cross-sectional view of the flex circuit 100 in a foldedposition. To facilitate use in a small volume, the outer branches 112and 113 are folded over the center branch 114, as shown in FIG. 4.Referring to FIG. 3, a sample fold line A—A is shown for the outerbranch 112. This maintains the appropriate density of leads whilefacilitating assembly. In the configuration shown in FIG. 4, the branch112 is folded lower than the branch 113 with only a minimal overlap,however those of ordinary skill in the art will recognize the endlesspossibilities, for example folding the outer branched completely overone another or even rolling the outer branches 112 and 113. Duringassembly, the connections between the leads of the flex circuit 100 andthe cables 116 can be made while the flex circuit 100 is unfolded. Afterformation of all of the appropriate connections the flex circuit 100 canbe folded, rolled or whatever, prior to final assembly.

FIG. 5 is a cross-sectional view of a transesophageal probe 300 inaccordance with the preferred embodiment of the present invention. TheTEE probe 300 uses two of the flexible circuits 100 shown in FIG. 2.Those of ordinary skill in the art will recognize that the number offlexible circuits 100 required for any given probe is variable, two wasselect for this example to illustrate the use of multiple flexiblecircuits 100. The two flexible circuits are labeled 100 a and 100 b. Thetransesophageal (TEE) probe 300 is formed by a housing 332 with anattached lens 340 through which imaging is performed. The housing 332securely holds a transducer assembly behind the lens 340. As with priortransesophageal imaging probes, the probe 300 is connected to anelongated semi-flexible body (not shown, but may be as described withrespect to FIG. 1). The elongated semiflexible body is, in turn,connected to a probe handle (also not shown, but may be as describedwith respect to FIG. 1).

The transducer assembly includes a circuit board 322, having a first andsecond set of lands, affixed to an IC 324, also having a first andsecond set of lands. The IC 324 distributes the signals carried by thecables 116 to the matrix of transducer elements 322. Due to spaceconstraints, the attainable pitch of connections to the IC 324 and thenumber of required connections, connections (lands) are spread over twoedges of the IC 324. In accordance with the preferred embodiment of thepresent invention, the circuit board 322 acts as a pass through,interfacing a portion of the cables 116 with lands on the IC 324. Asshown in FIG. 5, the first end 110(1) of the first flex circuit 100(1)is connected to a first set of lands on a first edge of the circuitboard 322, using for example TAB bonding, while the first end 110(2) ofthe second flex circuit 100(2) is connected to the first set of lands onthe IC 324, using for example TAB bonding. The circuit board 322provides a set of traces that connect a first set of lands on one edgeof the circuit board 322 to a second set of lands on a second edge ofthe circuit board 322. The second set of lands on the circuit board 322are connected to a second set of lands on a second edge of the IC 324.

The IC 324 is preferably acoustically matched to the circuit board 322and bonded thereto using a thin epoxy bond. The use of the circuit board322 provides a transducer assembly with improved thermal conductivityand better acoustic properties than simply running the cable 100(1)directly to the second set of lands on the IC 324.

In the structure illustrated in FIG. 5, the circuit board 322 extendspast the IC 324, on at least one edge thereof, to provide two differentinput surfaces separated vertically and laterally. Preferably, thecircuit board 322 and the IC 324 are related to each other so as toprovide access for the cables 116 to two sets of lands, the first set onthe circuit board 322 and the first set on the IC 324. Preferably, thecircuit board 322 has a lateral area (lateral being the direction alongthe extend of the probe 300) greater than the IC 324. However, those ofordinary skill in the art will recognize that this need not be the case,in fact the circuit board 322 and the IC 324 could have the same lateralarea (with a staggered relationship) or the IC 324 could have thegreater lateral area

As noted, the IC 324 is provided with at least two set of lands,preferably on at least two edges thereof, and more preferably atopposite ends thereof. The first set of lands has a pitch equivalent tothe pitch of leads 110(2)a-110(2)n on the first end 110(2) of the flexcircuit 100(2) and is positioned within the probe 300 to facilitateconnection thereto. Similarly, the circuit board 322 is provided with atleast two set of lands, preferably on at least two edges thereof, andmore preferably on opposite ends thereof. The first set of lands has apitch equivalent to the density of leads 110(1)a-110(1)n on the firstend 110(1) of the flex circuit 100(1) and is positioned within the probe300 to facilitate connection thereto. The pitch on the second set oflands on the IC 324 and the circuit board 322 are dictated by thetechnology used to form the connection.

For example, the IC 324 and the circuit board 322 may be electricallyconnected by a plurality of wires 326 (only one of which, 326 a, can beseen in FIG. 5) extending between the second set of lands on the IC 324and the second set of lands on the circuit board 322. TAB bonding, whichsupports a pitch of 100 micrometers, is one preferred way to form thisof connection.

Those of ordinary skill in the art will appreciate that the circuitboard 322 may be replaced with multiple circuit boards depending on therequired number of leads. Each additional circuit board could protrude alittle further out on both lateral ends to provide the necessary landspace for the formation of connections.

The circuit board 322 and the IC 324 are part of a transducer assemblywhich can be thought of as a stack of layers, sometimes referred to as atransducer stack. A first block 328, preferably made of heat dissipatingmaterial, may be situated above the IC 324, while a second block 336,also preferably made of heat dissipating material, may be situated belowthe circuit board 322. The materials forming the blocks 328 and 336 arealso selected based on desired acoustic properties as is known to thoseof ordinary skill in the art. For example, it is often desirable toabsorb vibrations, which would lead one of ordinary skill in the art toform the blocks 328 and 336 of acoustically absorptive material.

The connection between the IC 324 and the matrix of transducer elementsis beyond the scope of the present invention. Details of suchconnections can be found in co-pending U.S. patent application Ser. No.09/919,470, entitled System for Attaching an Acoustic Element to anIntegrated Circuit, assigned to the assignee of the present applicationand incorporated herein by reference. An alternative methodology forsuch a connection can be found in U.S. Pat. No. 5,267,221. Accordingly,only the briefest of explanations is presented herein.

A connection 334 provides electrical connectivity to the matrix oftransducer elements 332 using, for example, a plurality of leads. Aredistribution system 330 connects the leads of the connection 334 tothe individual elements of the matrix of transducer elements 332. Theredistribution layer may also be constructed so as to provides supportand some acoustic isolation for the matrix of transducer elements 332and may act as a layer of backing material. The physical structure ofthe connection 334, and in particular the redistribution system, may beany of a variety of known structures for connecting an IC to a matrix oftransducer elements. Co-pending U.S. patent application Ser. No.09/919,470, assigned to the assignee of the present application,entitled System for Attaching an Acoustic Element to an IntegratedCircuit describes a method and apparatus for forming such a connection,including the use of a re-distribution layer to match the pitch of theIC 324 with the pitch of the matrix of transducer elements 332. As shownin the co-pending application, the circuit board 322 and IC 324 can beplaced next to the matrix of transducer elements 332 rather than beingseparated by the block 328. The order and placement of the variouscomponents in the transducer stack may vary based on design and productgoals. Currently, one of the more important goals of transducer designis thermal management. Accordingly, the configuration shown in theco-pending application may in fact provide superior thermal connectivityand management. In the present application, the circuit board 322 and IC324 as shown separated from the IC 324 simply for ease of explanation.

The structure shown in FIG. 5 permits the connection of a large number(>100) of leads to the matrix of elements 130 in a relativelyconstrained area by using the circuit board 322 to provide, in effect,another set of lands in close proximity to the first set of lands on theIC 324. An additional benefit of the configuration disclosed in FIG. 5is modularization providing for more efficient assembly of the TEE probeas a whole. The illustrated configuration also promotes efficient heatdissipation and sound absorption.

FIGS. 6 and 7 show alternative views of the TEE probe 300. FIG. 6 is atop down cross-sectional view of the TEE probe 300 shown in FIG. 5 inaccordance with the preferred embodiment of the present invention. FIG.7 is a cross-sectional view of the TEE probe 300 of FIG. 5 taken alongline B—B shown in FIG. 6.

FIG. 8 is a diagram of connections between the flexible circuits 100(1)and 100(2) shown in FIG. 5 and the circuit board 322 and IC 324 alsoshown in FIG. 5. The circuit board 322 is supported by the block 336 andconnected to the IC 324 via a thin epoxy bond 338 which extends past thearea of interface, but not so far as to interfere with the connection ofthe flex circuit 100(1) with the circuit board 322. As noted, the firstend 110(1) of the flex circuit 100(1) is provided with overhanging orcantilevered leads 140 so as to permit the formation of a TAB bond withlands 342 on the circuit board 322. Similarly, the end 110(2) of theflex circuit 100(2) is provided with overhanging or cantilevered leads144 so as to permit the formation of a TAB bond with lands 346 on the IC324. If the flex circuit 100(2) contains a ground plane, the groundplane can be connected to the IC 324 using a variety of means, includingthe use of a additional wire or by dedicating a wire within the flexcircuit 100(2) to the ground plane. Similar arrangements can be madewith the flex circuit 100(1) to provide a ground plane therefor.

FIG. 9 is a diagram of connections between the circuit board 322 shownin FIG. 5 and the IC 324 also shown in FIG. 5. For each lead to beconnected to the IC 324 a wire 326 n is bonded (for example using a wirebond, an ultrasonic bond, a thermosonic bond or a ball bond) to a land342 n on the circuit board 322 and the corresponding land 344 n on theIC 324. While FIG. 9 only shows a single wire 326 a, those of ordinaryskill in the art will recognize that a plurality of wires would be used,preferably at least one per lead on the flex circuit 100(1), e.g. 80.Those of ordinary skill in the art will recognize equivalent structuresfor the wires 326, including for example flex circuits or ribbon cables.Further, if the flex circuit is provided with a ground plan, asdiscussed herein above, an additional trace on the bottom of the circuitboard 322 can be provided to bring the signal path to the opposite endthereof. Such a ground trace can be brought to the top of the circuitboard 322, for connection to the IC 324, in a variety of known manners,including an extra wire, a pass through etc . . .

Although a preferred embodiment of the present invention has been shownand described, it will be appreciated by those skilled in the art thatchanges may be made in such embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A method of wiring an integrated circuit (IC) having a first andsecond set of lands on respective first and second different areasthereof, the method comprising: electrically connecting first ends ofelectrical traces on a circuit board to the first set of lands on the ICin the first area; connecting a first flex circuit to second ends of theelectrical traces on the circuit board, the second ends disposed inclose proximity to the second area of the IC and wherein the first flexcircuit couples to the first set of lands on the IC in the first areavia the electrical traces on the circuit board; and connecting a secondflex circuit to the second set of lands on the IC in the second area. 2.The method of claim 1, further comprising: bonding the circuit board toa surface of the IC.
 3. The method of claim 1, further comprising:connecting the IC to a matrix of transducer elements.
 4. The method ofclaim 1, further comprising: connecting the first and second flexcircuits to a plurality of wires.
 5. The method of claim 4, furthercomprising: folding an end of the first flex circuit connected to theplurality of wires to reduce a width of a connection area proximate theend of the first flex circuit and the plurality of wires.
 6. The methodof claim 4, wherein the first flex circuit includes a first end havingleads with a first density for being coupled to the second ends of theelectrical traces on the circuit board, the first flex circuit furtherhaving a second end divided into branches, wherein each of the branchesincludes leads with a density less than the first density.
 7. The methodof claim 6, wherein the second end of the first flex circuit connects toa first portion of the plurality of wires, further comprising: foldingthe second end of the first flex circuit to reduce a width of aconnection area proximate the second end of the first flex circuit andthe first portion of the plurality of wires.
 8. The method of claim 7,wherein the second end of the first flex circuit includes a first outerbranch, a second outer branch, and a center branch, further comprising:folding the first outer branch and the second outer branch over thecenter branch.
 9. The method of claim 1, wherein connecting the firstflex circuit to second ends of electrical traces on the circuit boardincludes TAB bonding.
 10. The method of claim 4, wherein the second flexcircuit includes a first end having leads with a first density for beingcoupled to the first set of lands on the IC, the second flex circuitfurther having a second end divided into branches, wherein each of thebranches includes leads with a density less than the first density. 11.The method of claim 10, wherein the second end of the second flexcircuit connects to a second portion of the plurality of wires, furthercomprising: folding the second end of the second flex circuit to reducea width of a connection area proximate the second end of the second flexcircuit and the second portion of the plurality of wires.
 12. The methodof claim 11, wherein the second end of the second flex circuit includesa first outer branch, a second outer branch, and a center branch,further comprising: folding the first outer branch and the second outerbranch over the center branch.
 13. The method of claim 1, whereinconnecting the second flex circuit to the second set of lands on the ICincludes TAB bonding.
 14. The method of claim 1, wherein the second endsof the electrical traces on the circuit board include lands in closeproximity to the second set of lands on the IC.
 15. The method of claim1, wherein the IC and the circuit board are acoustically matched, themethod further comprising: bonding the IC to the circuit board using anepoxy bond.